J. Comp. & Math. Sci. Vol.2 (3), 457-462 (2011)
A Study on Call Admission Control Mechanisms for Wireless Communication Network SHAILESH JALOREE1, SUSHIL KUMAR VERMA2 and SACHIN KAMLEY3 1
Associate professor, Department of Applied Maths and Computer Science S.A.T.I, Vidisha. (M.P.), India. 2,3 Lecturer, Department of Computer Applications, S.A.T.I, Vidisha. (M.P.), India ABSTRACT Call admission control is a key element in the provision of guaranteed quality of service in wireless networks. Call admission control is a technique to provide QoS in a network by restricting the access to network resources. Simply stated, an admission control mechanism accepts a new call request provided there are adequate free resources to meet the QoS requirement of the new call request without violating the committed QoS of already accepted calls. With the constant increase in number of voice over packet network users, quality of service becomes crucial for the success of this type of real time applications. One of the quality of service techniques plays an important role: a decision process that takes place in voice gateways and is responsible of allowing calls only when expected level of performance in the network can be assured2. The design of all admission control algorithms for mobile cellular networks is especially challenging given the limited and highly variable resources and the mobility of users encountered in such networks. This article provides a study of admission control mechanism for cellular networks and also describes comparisons between call admission control mechanisms. Keywords: Call admission control, Quality of service, Wireless network, Base station, and RSVP.
1. INTRODUCTION Wireless communication networks have been expected fully utilization of network resources while retaining
satisfactory quality of service for each user. A wireless network is typically organized into geographical regions called cells2. The mobile user in a cell is served by a Base Station. Before a mobile user is
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communicating with other users in the network, a connection must be established between the users. The establishment and maintenance of a connection in a wireless network is the responsibility of the Base Station. When a user moves form one cell to another, The Base Station in the new cell must take responsibility of all the previously established connection3. A significant part of this responsibility involves allocating sufficient resources in the cell to maintain the QoS needs of the established connections. To satisfy these requirements Call Admission Control has been one of the potential solutions. Call Admission Control is required to consume a minimum of time and space to make call acceptance decisions based on various QoS requirements. It is worthwhile to mention the important contribution made in recent past by several researchers. Analyses Hierarchical cellular system with reneging and dropping for waiting new calls and handoff calls. Peha and Sutivong (1999) evaluates call admission control algorithms for a for cellular or microcellular system. MingHsing and Bassiouni (2000) proposed predictive schemes for handoff prioritization in cellular networks based on mobile positioning. Hou and Fang (2001) presented mobility based call admission control schemes for wireless mobile networks. Haung and Ho (2000) proposed a distributed call admission algorithm to provide QoS guarantees for multimedia traffic carried in a heterogeneous PCS network. Saraswat et al (2003) proposed a prioritized channel assignment scheme (SRS) for PCS. With the recent advances of wireless communication and mobile networking and the increasing demand of wireless services,
future generations of mobile networks ( such as Universal Mobile Telecommunication System (UMTS) among others) will focus upon enhancing the delivery of multiservices, such as voice, data , and multimedia, over existing and future generation of wireless and mobile infrastructures6. Each service requires a certain level of quality of service; e.g., when we refer to voice calls, the transit delay is one of the most important criteria, one must to deal with; when we refer to data, the packet losses are an important metric to consider, while for multimedia services, both transit delay and the packet losses are relevant in this case. It is well known that Call Admission Control is basically a provisioning strategy that limits the number of call connections into the network in order to reduce both congestion and call dropping4. Quality of service (QoS) provisioning in wireless networks is challenging problem due to the scarcity of wireless resources, i.e. radio channels, and the mobility of users1. Call Admission Control (CAC) is a fundamental mechanism used for QoS provisioning in a network. It restricts the access to the network based on resource availability in order to prevent network congestion and service degradation for already supported users5. A new call request is accepted if there are enough idle resources to meet the QoS requirements of the new call without violating the QoS for already accepted calls. With respect to the layered network architecture, different qualities of service parameters are involved at different layers. At physical layer, bit – level QoS parameters such as bit energy- tonoise density describe the quality of services
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Shailesh Jaloree, et al., J. Comp. & Math. Sci. Vol.2 (3), 457-462 (2011)
a mobile user receives4. In packet – based communication systems, packet-level QoS parameters such as packet loss, delay and jitter characterize the perceived quality of service. 2. CATEGORIES OF CAC MECHANISMS CAC mechanisms can be grouped in three main categories1. Local CAC mechanism. 2. Measurement based CAC mechanism. 3. Resource based CAC mechanism. Local CAC mechanism – Local CAC mechanism function on the outgoing gateway. The CAC decision is based on nodal information such as the state of the outgoing LAN or WAN link. if the local packet network link is down, there is no point in executing complex decision logic based on the state of the rest of the network, because that network is unreachable2. Local mechanisms include configuration items to disallow more than a fixed number of calls. For example, if the network designer already knows that no more than five calls can fit across the outgoing WAN link because of bandwidth limitations, than it seems logical that it should be possible to configure the local node to allow no more than five calls7. Measurement based CAC mechanism Measurement –based CAC techniques look ahead into the packet network to gauge the state of the network in order to determine whether to allow a new call. Gauging the state of the network implies sending probes to the destination IP address (usually the terminating gateway or terminating gatekeeper) that will return to the outgoing
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gateway with some measured information on the conditions the probe found while traversing the network to the destination. Typically, loss and delay characteristics are the interesting information elements for voice3. Resource based CAC mechanism- There are two types of resource – based mechanism: those that calculate resources needed and/or available, and those reserving resources for the call2. Resources of interest include link bandwidth, DSPs and DSO time slots on the connecting TDM trunks, CPU power, and memory. Several of these resources could be constrained at any one or more of the nodes the call will traverse to its destination. There are two additional categories of CAC functionality, but they do not address network design or infrastructure issues and therefore are not discussed in this document. These two CAC. Categories – security and user – focus instead on the policy question of whether the call user is allowed to use the network, as follows: Security – Is this a legitimate device or gateway on the network? There are authentication mechanisms, including protocols such as H.235, to cover this aspect of CAC2. User – Is this end user authorized to use the network? There are CLID/ANI and PIN verification methods, typically done via interactive voice response (IVR), to verify authorization3. The main difference exists between local mechanisms and other CAC mechanisms consider the local conditions of the gateway. It’s biggest lack is that it doesn’t take into account the topology of the network, so it can’t provide protection for
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the nodes and link s in the topology2. In other words it is not aware of the problems that occur in the topology. Other two categories of mechanisms are non – local, they look ahead the network to see whether the condition of the network is likely to ensure the desired quality of service for the call3. Measurement based techniques look ahead into the packet network bay sending probes to the destination IP address (in case of VoIP). Those probes return to its source with the information on the condition of network, typically loss and delay characteristics and then the CAC decision process uses that information for allowing or denying the call7. In case CAC denies the call, originating gateway can reroute the call if any other route is usable. There are two types of resource – based mechanism. First types are mechanisms that calculate needed resource and the other are mechanisms that reserve the resources along the path of the call3. 3. COMPARISION BETWEEN CAC MECHANISMS We will make this comparison based on a few criteria. We mentioned earlier that the basic difference against local CAC mechanisms is that these two categories have a certain awareness of the network conditions. Both of these types of – mechanisms allow the voice traffic to be accepted only when expected performance level can be assured2. However, measurement – based mechanisms are sending packet probes to a terminating Gateway’s IP address, and have no knowledge of nodes or bandwidth availability of links between the originating and the terminating gateway. This advantage of; the resource reservation
based mechanisms can be a pitfall because the customer has to own the WAN backbone in order to implement this feature on every node in the backbone (end to end), if he can’t do this, using these mechanisms can be very impractical, while measurement probes can be sent over any network (WAN, service provider’s backbone, internet) as we said before any call is accepted, there has to be decision process3. This decision process, either network probe testing or resource reservation process, increases what is called a post – dial delay. Measurement based mechanisms increase the post dial delay only for the first call for a specific destination, from that point information on that Destination is cached and a periodic probe is sent to the destination. This also has a bad side, because the periodic rate of probes can potentially admit calls when bandwidth is insufficient and can’t recognize non-gradual traffic fluctuations, so the quality of the call depends on the effectiveness of the other quality of service mechanisms in the network7. Resource reservation based mechanisms increase the post dial delay for every call, because reservation must be established before the cal setup can be completed2. However, once the call is established, bandwidth for the call along the entire path for the duration of the entire cal is guaranteed, and the quality of the call is unaffected by changes in network conditions. There is one more important issue regarding this comparison and that is scalability. Sending probes to a large number of individual IP destinations might be impractical. However, because WAN links are likely to be congested than the LAN network, it is possible to send the probes to the WAN edge devices, providing
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Shailesh Jaloree, et al., J. Comp. & Math. Sci. Vol.2 (3), 457-462 (2011)
a certain amount of scalability when using resources reservation based mechanisms, the flow reservation is crucial on the small bandwidth links and might not make sense on the large- bandwidth links in the backbone7. In this case hybrid networks topology can solve this problem. 4. NEW CALL ADMISSION CONTROL SCHEME The main aim of the new call admission control algorithm is to reduce the load on the system while reducing the dropping rates. In this algorithm, priority is given for handoff request, since handoff request is considered more important than new call request8. Let Ptot be the total power of the existing users, Let Pavail be the available total power. Let Lmax be the maximum overload of nonreal traffic class 1) accept a new call request 2) if it is handoff call, then 2.1) if Ptot<Pavail 2.1.1) Admit the request 2.2) If Ptot>Pavail 2.2.1) Degrade the existing users, as per their specification. 2.2.2) If still, Ptot>pavail 2.2.2.1.1) If Ptot<Lmax, admit the request 2.2.2.1.2) Otherwise reject the request. We apply the Service Degradation Descriptor (SDD) based on the degradation mechanism, in which user calls are degraded as per the SDD of the user requirement. SDD is a number between 0 and 5.If the SDD is larger, then the willing of the user/connection to be degraded is more and
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eventually dropped8. The real time services are prioritized over the non real time service which leads to reduced loss for real time traffic classes. 5. CONCLUSION In the recent years, there has been a tremendous growth of efforts in the research and development to provide mobile users the means of communication through wireless systems. Cellular mobile transmission is the latest and greatest front in the industry. Now the industry aim to provide integrated services through wireless mobile communication systems such as voice, data, images.paging,e-mail and multimedia services to the mass market. To support these types of services in wireless infrastructure, resource provisioning is a major issue. The one of the major issue is to control the call admission using some CAC schemes to reduce the congestion, call blocking and call droping by creating a limited number of call connections in the network.To cope with the requirements of desired quality of service call admission control schemes must have a balance provisions for call blocking and call dropping. The aim of our study is to provide better knowledge for call admission control mechanism that improves the performance of wireless mobile communication systems. Quality of service techniques is necessary for the success of a real time application such as VoIP. We emphasized a need for a call admission control on the outgoing (call originating) gateway, and showed the main differences between two â&#x20AC;&#x153;look aheadâ&#x20AC;? types of CAC Mechanism. The obvious advantages of measurement based CAC mechanisms are
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that the probes can be sent over any kind of IP network, and that is very scalable. Resource reservation based CAC mechanisms are more reliable in terms that the call’s quality is preserved even when changes of network traffic conditions occur. Scalability of resource reservation based CAC mechanisms should be resolved using hybrid network, for example, combining RSVP with Diffserv. 6. REFERENCES 1. A. Suitvong and Jon M.Peha,”Novel heuristics for call admission control in cellular systems” Proc. IEEE 6th international Conference on Universal Personal Communications Record, Vol.1, pp.129-133, (1997). 2. J. Dvidson, et al., Deploying CISCO Voice over IP solutions”, Cisco press, indiaapolis, IN, (2002). 3. J. Davidson, “Voice over IP fundamentals”, Cisco press, Indianpolis,
IN, (2000). 4. S. Herzog,”RSPV Extensions for policy control”, RFC 2750, January (2000). 5. R. Barden, Ed., L. Zhang, S. Berson, S. Herzog, S. Jamin,” Resource Reservation Protocol (RSVP)-version 1 Functional Specification” RFC 2205, September (1997). 6. R. Ramjee, D. Towsley, and R. Nagarajan, “On optimal call admission control in cellular networks,” Wireless Networks, Vol.3, no.1. pp. 29-41, Mar. (1997). 7. Vedran Srsen, Petar Knezevic, and Kresimir Segaric. “A comparison between two types of call admission control mechanisms” EUROCON, Ljubljana, Slovenia (2003). 8. N. Mohan, T. Ravichandran. “An efficient multiclass call admission control and adaptive scheduling for WCDMA wireless network”, EJSR ISSN 1450-216X Vol.33 No.4, pp.718-727 (2009).
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